Control system.



R. E. HELLMUND.

CONTROL SYSTEM.

APPLICATION FILED SEPT. 25, I914.

1,249,954. Patented Dec. 11,1917.

3 SHEETSSHEET l.

Ground Grou/m.

' I v a INVENTOR W v fiudo/ mw/mm 25 BY w W 22"4 V ATTORNEY I D's/lay R. E. HELLMUND.

CONTROL SYSTEM.

APPLICATION FILED SEPT. 25, 1914.

1,249,954. Patented Dec.11,1917.

3 SHEETSSHEET 3- F/e; A9.

TNIESSES: INVENTOR- I Pz/do/f EHN/mund.

I ATTORNEY UNITED STATES PATENT orrion.

BUDOLF E. HELLMUND, 0F PITTSBUItGH, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC AND MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- VANIA Specification of Letters Patent.

CONTROL SYSTEM.

To all whom it may concern:

Be it known that I, RoooLr E. HELL- MUND, a subject of the German Empire, and a resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Control Systems, of which the following 15 a specification.

My invention relates to systems of control, and it has special reference to means for preventing the occurrence of flash-over conditions in dynamo electric machines, more particularly electric railway motors, under predetermined conditions.

The object of my invention is to provlde simple and reliable means of the above-indicated character which shall efiectively obviate the possibility of flash-over of electric motors upon the resumption of supplycircuit voltage after a temporary interruption thereof, such as is caused b the trolley wheel or other current-collecting member passing under a section break or otherwise momentarily leaving the supply-circuit conductor. I

More particularly, in high-voltage direct current systems and in the case of locomotives of large capacity, it may be advisable, for economical and other reasons, to provide means for preventing flash-over of the motor, the most common cause of which is the sudden resumption of supplycircuit energy after the temporary interruption thereof at section breaks, etc. Whenever the su ply of energy is resumed, a heavy rush 0 current through the deenergized motor windings occurs, which causes great field-flux distortion and relatively high voltage between commutator segments. This condition arises by reason of the fact that the flux set up by the armature current, upon resumption of supply-circuit energy, readily traverses the entirely laminated armature core, and, consequently, builds up to a normal value much more rapidly than the main field flux which encounters the high magnetic reluctance of the solid iron or steel frame castings and which is, therefore, partly damped out by eddy currents.

According to my present invention, I provide various modifications of means for obviating the above-mentioned operating dif -matically. Injurious arcin Patented Dec.11,1917.

source of energy when the supply-circuit energy is temporarily interrupted. The

main field flux 1s thus maintained at a pre- 1 determined value during the'interruption and, as a, result, when the supply-circuit energy .is resumed, the predominance of,

armature ampere-turns over field ampereturns 1s prevented, and flash-over cond1- tions do not obtain.

vention comprises the use of a small auxilthe main field winding from the generator end of the machine will be maintained for a predetermined period. Longer energy interruptions may be provided for by means of suitable automatic devices for switching in an independent source of energy to supply current. to the main field winding at the end of the said period.

Moreover, systems of the class mentioned have an additional advantage of flexibility of operation, in that the field current and, consequently, the armature voltage may be increased to cause the'current in the motor circuit to assume a relatively low value, substantially zero if desired, before the motor circuit switches connected to the supply circuit are opened, either manually or autoin the switches may thus be entirely avoi ed.

' In the accompanying drawings, Figures 1 to 11, inclusive, are diagrammatic main circuit views of the control systems embodying various forms of my invention; Fig. 12 is a diagrammatic view of an auxiliarycontrol system for governing the main-circuit system of Fig. 11 .in accordance with the sequence chart, of well-known form, shown in Fig. 13; Fig. 14 is a diagrammatic view of a modification of my invention; Figs. 15, 16, and 17 are views, respectively similar to Figs. 11, 12 and 13, of another modification of my invention; and Figs. 18 and 19 are diagrammatic views of further modifications thereof; Like reference characters designate like parts in-all of the figures.

Referring to Fig. l of the drawing, the

In one form, my insystem shown comprises a supply-circuit conductor marked Trolley, a return 011'- cuit conductor marked Ground, an electric battery B, that is variably connected to the part F of the field winding.

Any familiar and suitable form of novoltage release switch, with a graduated return to prevent disconnection of the auxiliary source of energy before the field is properly built up, may be employed. The switch may take a form similar to that illustrated in Fig. 2 and described below. Whereas, for the sake of simplicity and clearness, the switch in question is not illustrated in the other systems shown, it will be understood that it is preferably employe in the various systems. The system illustrated in Fig. 2 comprises, in addition to the apparatus shown in Fig. 1, a no-voltage release switch NV, and a portion of a motor-controlling switch CS, the complete connections of which are omitted, for the sake of simplicity. When the series-connected actuating coil 1 of the switch NV is energized from the supply circuit, the switch assumes its upper position shown in the drawing, in opposition to the momentary action of the dash-post 2 or other suitable retarding means. The armature and the two portions of the field winding are then connected in series-circuit relation. Upon the failure of the supply circuit voltage,-the switch drops to its lower position, thereupon disconnecting the part it of the field winding from the motor circuit and connecting it to the battery B, provided the controlling-switch CS occupies any on position; such field connections, of-

course, not being desired when the motor is voluntarily disconnected from the supply circuit.

Assuming that, upon a temporary interruption of supply-circuit voltage, the parts of the systems shown occupy their respective emergency positions, the operation thereof, which, it will be understood will apply, in a general sense, to the various other systems to be hereinafter described, may be set forth as follows: the temporary battery connection maintains the field flux at any desired value during the interruption. l Vhen the supply-circuit energy is resumed, the field ampere-turns will thus immediately be of a normal or other predetermined value, irrespective of the slow building up of the field flux by the motor current. The predominance of armature ampere-turns over field ampere-turns is prevented in this way, and ash-over conditions do not obtain.

The system illustrated in Fig. 3 comprises a supply circuit and an electric motor similar to those shown in Figs. 1 and 2; a small motor-generator or, preferably, a dynamotor of familiar form which is customarily employed for control and lighting purposes in many types of locomotives; a battery B; a portion of a controlling-switch C; and a novoltage graduated release switch NV.

The dynamotor preferably comprises a motor armature winding DM, and a generator armature winding DGr that are mounted on a common shaft S, a. series-connected field magnet winding 3 and a second field magnetwinding 4 that is connected in parallel with the generator armature. The machine is either designed to have relatively great flywheel effect or is provided with a suitable flywheel FVV. Energy is supplied to the, dynamotor from the supply circuit through cotiperating stationary and movable contact members 5 and 5 of the switch NV when in its lower position or energized condition; and the generator armature winding DG is connected through a suitable variable resistor 6 across the portion F of the main field magnet winding.

The controlling-switch C may take any l .usual form, and, for the sake of clearness and simplicity, only the portion thereof that I employ in efiecting the preventive action under consideration is illustrated. The novoltage release switch NV may be of any suitable form, such as that illustrated in Fig. 2, with the addition of means, such as a spring 7, for biasing the switch to its upper position, for example, for a purpose to be described.

Assuming that, just prior to an interruption of supply-circuit energy, the various parts of the system occupy their respective illustrated positions, the operation of the system may be briefly described as follows: The fly-wheel effect of the dynamotor will maintain. a suitable rotative speed thereof, and, consequently, energization of the portion F of the main field winding for a predetermined period of time, which will usually extend until supply-circuit energy is resumed. However, if the energy is interrupted for a longer period, then the denergized no-voltage graduated release switch, actuated by the biasing spring 7, reaches its upper position, wherein the mo able contact member 5 makes contact with a pair of stationary contact members 8. A circuit is thereby established from one side of the battery B, through conductor 9, the portion F of the main field winding, the

Mill

lie

resistor 6 to ground, and from ground,

7 it of the controlling switch C in any operative position and conductor 15 to the other side of the battery B.

The field winding 1.

It may be observed at this time that the systems hereinbefore described, as well as several of the systems to be set forth, are

readily adapted for'use in the well-known field control systems.- The excitation of the field winding F may be easily regulated by the variation of the number of active cells of the systems shown in Fig. 1 and in Fig. 2, and of the resistor 6-in Fig. 3. Moreover, a separately excited.portion 'of the main field winding may be of advantage in limiting the maximum speed of the motordriven vehicle to any desired value.

The system illustrated in Fig. 4 comprises a supplv circuit and a main motor similar to those shown in Fig. 3, a. battery B, and a motor-generator set driven from the battery and connected to energize the portion F of the main field winding during temporary interruptions of the supply-circuit energy. The motor-generator set comprises a driving motor M having a shunt field winding 16 that may be regulated by a suitable resistor 17, and a generator G having a shunt fieldwinding 18 that maybe varied by a resistor 19. In this case, field control of the main motor may be readily effected by variation of the field resistors 17 and 19 or of the battery B. It will be understood that, whenever a dynamotor is available, the generator G may be coupled directly there to, and the motor M and battery B may be omitted. Where a battery is used, it may again be charged from the main motor circuit, as in Fig. 1, for example, if desired. In another aspect, the exciting generator G may be driven by a gas engine or other prime mover.

In Fig. 5, a small dynamotor-electric machine E is connected across a predetermined part of the main motor field winding, and is provided with a variable shunt field winding 20 and a fiywheel FW. While the main motor is operating normally, the machine E will be driven from the field-Winding voltage as a motor. Upon interruption of the supply-circuit energy, the fly-wheel eifect of the machine E will keep it running as a.

generator to excite the main winding for a predetermined period of time. If desired, an automatic arrangement for maintaining a longer energization of the main field winding, whenever necessary, such as that illustrated in Fig. 3, may be employed.

The system shown in Fig. 6 comprises a suitable supply circuit; a main propelling motor having an armature A and a singlepart main field winding F; and a motor-- generator set having a motor M that is driven from a variable battery B and is provided with a variable shunt field winding 16 which may be reversed by asuitfible re- 1 versing switch RS, and a generator G that is provided with a variable shunt field winding 18 and a series field winding21 which is connected in circuit with the main armature A, and that is connected, as a whole, to energize the main field winding F.

Although no part of the field windingF is connected in circuit with the main motor armature A during emergency conditions,

the series characteristic of the main motor is,

nevertheless, maintained to a very large extent by the use of the series connected field winding ofthe generator G. The shunt field winding 18 is merely strong enough to maintain a predetermined energization of the main field winding F upon a temporary interruption of suppl circuit energy, and is also adapted to permit of ready means for field control, if desired.

However, the generator field winding 18 may be omitted in many cases, because, with very short interruptions of energy, the selfinduction of the main field winding F will prevent the field currentfrom dying out rapidly. Longer interruption of supply-circuit voltage may becompensated for by means of a suitable automatic switching device, such as is illustrated in Fig. 3. In case the shunt field winding 18 is omitted, a very desirable series characteristic may be obtained for the main motors, and field control may be conveniently efiected through changes in the speed of the motor M by variation of its shunt field-winding current or of the battery voltage. Wherever a dynamotor is available, the generator G may be mechanically connected thereto, as illustrated in Fig. 7, and the speed of the dynamotor may be varied by manipulating its shunt field winding 4. It should be noted that the latter case is relatively simple in that the method of field control permits of the omission of a number of the main-circuit switches that are employed in many systems of the prior art.

Moreover, the customarily employed maincircuit reversing switchmay be omitted, by

the utilization of the small motor-field reversing switch RS, as in Fig. 6, to reverse the direction of rotation of the motor-genermain-circuit current through the generator field winding 21 is also preferably employed.

It will also be understood that, in the case of interpole motors, the interpole field windings may be treated similarly to the main field windings in the system of Fig. 6 and in several of the other systems, if desired.

In Fig. 8 is shown a system quite similar to that illustrated in Fig. 6, the chief differences residing in the provision of a 00- operating series field winding 22 for the motor M. In several of the above-described systems, the main field winding F would be only partially energized upon interruption of the supply-circuit energy. In the-system under consideration, the field windings of the auxiliary motor M are designed so that, even with a relatively small load on the main motor, the motor M has a highly saturated field, and, therefore, the speed of the motorgenerator set will change very little with the main motor load. Thus, under normal operating conditions, the series field winding 22 of the auxiliary motor has relatively small influence upon the characteristic curves of the main motor. However, if the main current is interrupted, a relatively weak field flux is supplied by the shunt field winding 16 alone, thereby increasing the speed of the motor-generator set and, consequently, increasing the energizing current of the main field winding F to any desired extent. When supply-circuit energy is resumed, the main motor has a relatively strong field fiux already established. The system just described will compensate for either temporary or relatively long supply-circuit energy interruptions. In case of short interruptions, the field strength of the main motor is maintained through the agency of the selfinduction of the field windings F and 18; while, in case of longer interruptions, the main field strength is. maintained as just recited. Tf desired, the battery B may, in this system, as in several others shown, be charged from the main circuit, by opening a switch 8 and closing a switch 8, or the generator field winding 18 may be excited from the battery B, if desired. 7

The system illustrated in Fig, 9 comprises a suitable supply circuit, the main motor having the armature A and the field winding F, a main circuit variable resistor R, and a dynamotor having a motor armature winding DM, a generator armature winding DG, a shunt-connected field winding 23, and a field winding 23 that is connected in series with the generator armature DG and a variable resistor 2-across the main field winding F. The dynamotor may be connected in series with a variable resistor 25. The dynamotor field windings 23 and 28 are disposed to act differentially under emergency conditions.

The operation of the system under consideration may be briefly set forth as follows: When the main motor is being accelerated by varying the resistor R, in accordance with customary practice, a portion of the main current traverses the generator armature winding DG and the associated field windin 23*,the field windings 23 and 23 thus being adapted to aid each other to produce a relatively strong field fiux in the dynamotor, thereby causing it to run at a relatively slow speed. In case of interruption of the supply-circuit energy, however, the generator armature DG will supply current to the main field winding F in the same direction as before, thus effecting a reversal of the current in the armature DG and in the field winding 23.

The ensuing difierential action between the dynamotor field windings produces a relatively weak field flux in the machine, with acorresponding increase of speed to effect a predetermined energization of the main field winding F. When supply-circuit energy is resumed, the current through the generator Will reverse again, and, since the .dynamotor is running at a relatively high speed, the voltage across the field winding F at the time will be sufficiently high to efifect a rapid building up of the main field fluxto-its normal value.

Fig. 10 discloses another modification, wherein the series field winding 22 of the auxiliary motor M is adapted to act differentially with respect to the shunt field winding 16. The generator G, asshown, has the series field winding 21. The main armature A is connected to the supply circuit through a portion of a control switch CS and a resistor R, which is paralleled by the cooperating stationary and movable contact members 26 and 27, respectively, of a no-voltage graduated releas switch NV". The series-connected actuating coil 28 of the switch, when energized through the control switch CS is adapted to maintain contact between the contact members 26 and 27, which contact is not broken until a spring member 7 within the dash-pot 2 separates these contact members a predetermined period of time after the interruption of supplycircuit energy.

The system just described, while not suitable for maintaining the main field energization, as set forth in connection with. the system shown in Fig. 8, during relatively long energy interruptions, will however, produce a relatively steep main-motor speed clgaracteristic, which is usually very desira le. by reason of the fact that, whenever the armature current increases, the field-winding voltage and, therefore, the field current is increased, because of the increased excita- This steep characteristic is obtained as well as the increased speed of the motorgenerator set that is caused by the fieldweakening action of the differentially-com nected motor field windings 22 and 16.

The function of the resistor R and switch NV is'to act as a protective device in case of relatively long energy interruptions. Upon the denergization of the actuating coil 28 of the switch, the spring 7 gradually raises the movable contact member 27, unt1l the contact members 26 and 27 separate after a predetermined period of time. If supply circuit energy is then resumed, the interposition of the resistor R in circuit will prevent an excessive instantaneous flow of current, if the control switch CS still occu-v pies an operative position. The switch NV will then be closed by the energization of its actuating coil 28. As in Fig. 8, the battery may be charged from the main motor circuit, if desired, by opening the switch 8 and closing the switch 8 It should be understood that various modifications of the systems hereinbefore illustrated may be readily effected; for example, the generator series field winding 21 or the shunt field winding 18 may be omitted in some'cases, without materially varying the operation of the particular system.

Fig. 11 illustrates a system comprising a suitable supply circuit, the main motor having the armature A and the field winding F; the battery B which is connected in circuit with the motor; the auxiliar motorgenerator set having a motor M that is driven from the battery Band a generator G that is adapted to energize the main field winding F; a reversing switch RS for the,

armature A with respect to the field winding F and the motor-generator set and battery; an accelerating resistor AR, the sections of which are adapted to be respectively short-circuited by switches R, R and R"; and a plurality of main circuit switches LS and M The motor M is provided with a shunt field winding 16, while the generator G is provided with three field windings 18, 21 and 29. The shunt field winding 18 is connected in series with a resistor 30, the' sections of which are respectively adapt-' ed to be short-circuited by switches G and G the series field winding 21 is connected in' series-circuit relation with the main motor; and the field winding 29 is adapted to act differentially to the other two and is connected across the main armature A inseries with a resistor 31, the sections of which are respectively adapted to be short-circuited by switches A", A and A". All of the switches shown, with the excep tion of the switch LS, are preferably of a simple and familiar electromagnetically opeffected by initially closing switches LS, M

G and G then gradually and successively R R and R; further acceleration maybe secured by successively opening switches Gr and G to weaken the shunt field winding 18, and closing switches A A and A to strengthen the armature-excited, differentially-connected field winding 29, thereby in each case serving to further weaken the current in the main field winding F to 1ncrease the main motor speed. The auxiliary control'system illustrated in Fig. 12 is of a simple and familiar type that is adapted to actuate the several circuit switches as just described and, as indicated in the chart of Fig. 13, and, inasmuch as the particular system employed for arranging the circuit contion of the generator series field winding 21,. terated type, the actuating coils of which closing the 'resistor-short-circuiting switches nections of the system shown in Fig. 12 is r not material to my present invention, I have not deemed it necessary to describe the auxiliary control system in detail.

Assuming the motor to be running in its final operating condition, and that the actions of the generator field windings 18 and 29 are then exactly equal and opposite, so that the field winding 21 is alone active, the operation of the system with respect to the prevention of flash-over conditions may be described as follows: By reason of the neutralization of the generator field windings 18 and 29, the mainmotor will run with a straight series speed characteristic. Upon the interruption of supply-circuit energy, the main motor field excitation and the main armature voltage tend to decrease to zero. Consequently, the excitation of the armature-excited field winding 29 decreases,

with the result that the shunt field winding 18 exerts an active influence to produce a positive magnetization of the generator G, and, therefore, of the main field winding F to a .predetermined extent which will obviate an excessive rush of current when the supply-circuit energy is resumed.

The system shown has the further advantage of producing relatively steep speed characteristic curves, during acceleration. Since the generator field winding 29 is excited from the main armature A, the voltage impressed upon the field winding will increase as the main-circuit resistor is gradually short-circuited, thereby efi'ecting an automatic decrease of the current supplied by the generator G to the main field winding F as the main motor accelerates, by reason of the differential action of the field curves signify a relatively small number of requisite accelerating positions of a motorcontroller. As a modification of the system,

' the' generator field winding 29 may be conall 1 thereby The switch AS maintains its closed nccted across the supply circuit, by opening a switch 11 and closing a switch 11*, in which case, the type of characteristic curves referred to would not, of course, be obtained.

A further advantage of the various systems described herein, in which the main motor field winding is either partially or entirely excited from a separate source of energy, resides in their adaptability to provide means for interrupting the main motor circuit during motor operation when a substantially zero current obtains, and, consequently, without'arcing. For example, consider the system shown in Fig. 14, which comprises the system shown in Fig. 8, with the addition of an automatic switch'AS and a parallel-connected hand-operated switch ll-Lo. When it is desired to disconnect the main motor from the supply circuit, the auxiliary motor field winding 16 may be weakened to efitect an increased speed oi? the motongenerator set, or the generator winding 18 may be strengthened, or both, to increase the energization of the main field winding l5, thereby increasing the main armature voltage to a value that is substantially equal to-the voltage impressed upon the armature A from the supply circuit. in this manner, the motor current is reduced to practically a zero value, whereupon the circuit may be broken either manually or automatically in any suitable manner. Arcing and its ensuing deleterious results may thus be obviated. For instance,-the automatic switch AS, which comprises an actuating coil 32 and cooperating stationary and movable contact members 33 and 34l,respectively, that are all included in the main motor circuit, and a spring. member 35 for biasing the switch to the open position, may be employed. llhe hand-operated switch HS is connected in parallel relation with the contact members of the switch AS. For connecting the main motor to the supply circuit, the switch HS is initially closed, effecting the energization ot the actuating coil 32 of the switch AS, which then closes and connects its coiiperating contact members 33 and 34 in circuit with the main motor and the coil 32. For disconnecting the main motor from the supply circuit, the switch HS is opened, and the motor current is reduced to zero, as described above.

cs1- tion until the current absorbed from the 1 supply circuit assumes the low value referred to, when the switch automatically inan auxiliary motor-generator set comprising a motor M that is driven from a battery B in the main circuit, and a generator G that is connected to energize the main field winding F; an accelerating resistor AR, the sections of which are respectively adapted to be short-circuited by switches R R and R, which are preferably of a familiar electromagnetically actuated type; a line switch LS and an auxiliary motor-circuit switch K of similar form; and a reversing switch Es for reversing the electrical relations of the main armature and field winding.

The auxiliary motor M is provided with a shunt field winding 16, and a second field winding l0 that is connected in series-circuit relation with the main field winding l and the sections of which are respectively adapted to be short-circuited by switches X and X The generator G is provided with a shunt field winding 18 that is connected in series with a resistor 4-1, the sections of which are respectively adapted to be short-circuited by switches 6%", G and G, across the battery B, and with a series field winding 21 that is connected in seriescircuit relation with the main motor.

The auxiliary control system, out a familiar type, that is illustrated in Fig. 16, is adapted to actuate the various switches embodied in the system shown in Fig. 15 in accordance with the sequence chart. of Fig. 17 lnasmuch as the particular means for manipulating the main-circuit connections is not relevant to my invention, no detailed description thereof is deemed necessary.

The accelerating operation of the system shown in Fig. 15 may be briefly set forth as follows: Upon initial connection to the supply circuit, the switches LS and K are closed,

and the motor field winding t0 and the generator field resistor 41 are completely shortcircuited. The sections of the acceleratin resistor-are then successively short-circuite by the closure of the switches R R and R to gradually effect an increased main motor speed. The several field-controlling switches G", G and G and X andX are opened in that order to respectively efl'ect a weakening of the generator-field .flux and a strengthening of the auxiliary motor-field flux with its consequent motor-speed reduction, to thereby graduall decrease the excitation of the main fiel winding F, and thus increase the main motor speed. Inasmuch as yhe auxiliary motor field winding 40 is connected in series-circuit. relation with the main field winding F, the direction of t ll current traversing which is the same for a given dlrection of rotation, the auxiliary motor field winding- 40 will never have ation, and maintain a predetermined value thereof during the energy interruption.

Fig. 18 illustrates, by a simplified diagram, a system which difiers from that shown in Fig. 15 only in that the field winding of the auxiliary motor is connected in series with a variable resistort2 across the main field winding F, instead of in series therewith, as in the system of Fi 15. The operation of the system will e readily understood from the discussion given in accordance with Fig. 15.

If desired, instead of exciting the generator shunt field winding 18 from the bat-.

tery B, it may be energized from th main armature A. While the speed characteristic of the main motor will then be somewhat different, the operation of the systemrelative to temporary supply-circuit interruptions will be similar to that just set forth.

Wherever it is necessary or desirable to compensate for relatively long power interruptions, a protective system similar to that shown in Fig. 10 may be employed to automatically insert the resistor AB in circuit a predetermined length of time after the interruption of supply-circuit energy.

Fig. 19 discloses a system comprising a suitable supply circuit including conductors respectively marked Trolley and Ground the main motor having the armature A and the field magnet winding F; an accelerating resistor AR; and an auxiliary motor-generator set comprising a motor M, and a generator G that is adapted to energize the main field winding F. The purpose of this system is to effect the desired results under emergency conditions, without requiring the use of a battery or other auxiliary source of energy for the small motor, the armature thereof being connected across the main armature A and the accelerating resistor AR.

The motor M is also provided with a shunt field winding 16 which is adapted to be variably energized from the main armature A, and with a second field winding 22 that is connected in the main motor circuits. The

enerator G has a variable shunt field windmg 18 that is connected across the terminals of the armature of the small motor M, and a second field winding that is disposed in'tlie main motor circuit.

The prevention of flash-over conditions in the system just described, upon ,the re sumption of supply-circuit energy alter a temporary interruption thereof, is effected as follows: The 'deenergization of the generator field winding 21 tendsto decrease the excitation of the main field winding F, and, consequently, to decrease the voltage of the main armature A. However, the simultaneous deenergization of the auxiliary motor field winding 2:2 causes a corresponding increase in the speed of the motor-generator set-thereby tending to maintain a predetermined energization of the main field winding F.

It may. be observed here that several of the systems 'hereinbefore described, those shown in Figs. 15 and 19, for example, are also adapted for regenerative operation. However, such operation is not material to my present invention, and is, moreover, fully set forth in my copending application, Serial No. 87 66, filed August 7, 1914:.

I do not wish to be restricted to the specific circuit connections or arrangement of parts herein set forth, as various modifications may be made within the spirit and scope of my invention. Moreover, I desire it to be understood that, in employing the expression energize ,a predetermined part of the ,main field winding, or its equivalents, in the claims, I intendto signify any desired portion of the field winding, which may include the entire winding, in some instances. I also desire that only such limitations shall be imposed upon my invention as are indicated in the appended claims.

I claim as my invention:

1. In a control system, the combination "with a supply circuit and a motor having an armature and a field-magnet winding, of a dynamo-electric machine having field windings and associated with the motor field windings for varying the energization of the latter to prevent flash-over conditions in the moto and means associated with the machine eld windings for assisting in accelerating the motor.

*2. In a control system, a supply circuit,

ing a predetermined magnetic flux in -the machine to prevent fiaslnover conditlons upon a resumption of supply-circuitenergy and'means for automatically operating said dynamo-electric machine in accordance w1th the current flowing through said motor.

4. In a control system, a supply circult, an electric motor having anarmature and a field-magnet winding connected across the supply circuit and an auxiliary source of energy connected in series with said motor, of means energized by said auxiliary source of energy and governed by the current flowingv through said motor for,en erg1z1ng a predetermined part of said windin upon a temporary interruption of energy rom sald supply circuit. 5. In a contror'system, the combinatlon with a supply circuit, and an electric motor having an armature and a field magnet winding, of an auxiliary motor generator adapted to energize a predetermined part of said field Winding and having a set of differentially-connected field magnet windings to effect an increased energization of said first field winding from said machine upon a temporary interruption of energy from said supply circuit.

6. In a control system, the combination with a supply circuit, and an electric motor having an armature and a field magnet winding, of an auxiliary motor-generator adapted to energize a predetermined .part of said field winding and having difi'erentially acting series-connected and shunt-connected field magnet windings to effect an increased speed of said motor-generator and a consequent increased energization of said first field winding therefrom upon a temporary interruption of energy from said su ply circuit. I

In a control system, the combination with a supply circuit, and an electric motorhaving an armature and a field magnet winding, of an auxiliary source of energy and an auxiliary motor-generator connected thereto and adapted to energize a predetermined part of said field Winding and having a, plurality of field magnet windings respectively connected to said source of energy, in parallel with said armature and in series therewith, said last field magnet windings being arranged to act differentially to efi'ect an increased energization of said first field winding therefrom under predetermined conditions.

8. In a control system, the combination with a supply circuit, and an electric motor having an armature and a field magnet winding, of a storage battery connected in circuit with said motor, and an auxiliary motor-generator connected thereto and adapted to energise a predetermined part of said field winding and having a plurality of field magnet windingsrespectively connected to said source of energy, in parallel With said armature, and in series therewith, said last field winding being wound differentially to the other two field windings of the motorgenerator to effect an increased speed thereof and ,a consequent increased energization of the field winding of said motor therefrom upon a temporary interruption of energy machine'having a field-magnet winding, of

means comprising a dynamo-electric machine 7 for energizing a predetermined part of said. field winding upon a temporary interruption of the energy from said supply circuit.

11. In a control system, the combination with a supply circuit and an electric motor having an armature and' a field-magnet winding, of means comprising a motor-generator set for energizing a predetermined part of said field winding upon a temporary interruption of the energy from the supply circuit.

12. In a control system, the combination with a supply circuit and an electric motor having an armature and a field-magnet winding, of means comprising a generator having differentially connected fiel'd' magnet windings for effecting an increased energization of the motor in case the energy from said supply circuit be temporarily interrupted.

13. In a control system, the combination with a supply circuit and an electric motor having an armature and a field-magnet winding, of means comprising a motor-generator set having the generator armature thereof connected in shunt circuit to said motor field Winding for efi'ecting an in creased energization of said motor field winding by said generator upon a temporary interruption of energy from said supply circuit. p

In testimony whereof, I have hereunto subscribed my name this 22nd day of September, 1914.

nnno tr n. HELLM ND. Witnesses A. L. BnooMALL, B. B. Hines. 

